Meanwhile, the Steelers released James Harrison and Willie Colon in moves to get them under the salary cap.

With five openings in the starting lineup, the Steelers are clearly looking to make some changes coming off of an 8-8 season last year. But that does not seem to bother Pittsburgh's general manager Kevin Colbert, particularly the loss of Wallace, Lewis and Mendenhall (via the Pittsburgh Post-Gazette).

"Only time will tell...we'll see where that goes," Colbert said. "You can also argue we lost three persons from an 8-8 team."

Regardless of how Colbert feels about the Steelers’ losses so far, there is a clear need to replenish some depth at a several positions prior to the start of the draft.

Running Back

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The Steelers have already addressed one of their needs via free agency when they signed quarterback Bruce Gradkowski to back up Ben Roethlisberger. They will address another on Monday when they sign Matt Spaeth to add depth at tight end.

But one area that the Steelers may still need to address is at running back.

Running back has been an area of disappointment for the Steelers, and they will need to explore all avenues in order to upgrade the position.

Bradshaw is a proven running back who has had a productive career but has trouble staying healthy. Though he could come cheap, there is certainly a risk factor involved, and it's a risk the Steelers have taken before.

Back in 2004, the Steelers signed Duce Staley to help reinvigorate their ground game—which he did until injuries derailed his career.

The Steelers will not have much money to invest in a running back, but adding a veteran would help, as neither Jonathan Dwyer or Isaac Redman appear to be the type of back who can help carry the load.

Finding a stopgap veteran will allow the Steelers to select a running back later in the draft—or even take a risk on a player such as Marcus Lattimore—and slowly develop him.

There is no doubt that the Steelers need to upgrade the position, and free agency could provide a short-term answer.

Wide Receiver

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After exploring but declining the option of signing wide receiver Steve Breaston earlier this offseason, the Steelers are left with Antonio Brown, Jerricho Cotchery and Plaxico Burress under contract for the 2013 season.

The big question at this point, however, is the status of Emmanuel Sanders.

Sanders visited the New England Patriots, and there has been plenty of rumors flying around that he has signed an offer sheet, but that is not the case according to Gerry Dulac of the Pittsburgh Post-Gazette.

But if Sanders does decide to sign another team's offer sheet, there is a good chance that the Steelers may allow him to leave.

In three seasons, Sanders has just 94 receptions for 1,290 yards and five touchdowns. Even though he eventually became a significant part of the offense last season, he still finished with only 44 receptions.

Not that the potential loss of Sanders wouldn’t hurt, but in a relatively deep draft, the Steelers would be wise to allow Sanders to walk and receive a third-round selection as compensation.

If this does happen, the Steelers will need to fill Sanders' spot with a free-agent receiver. But even if he does remain with the Steelers, the team should still explore the option of signing a receiver to add more depth.

Nothing again against Cotchery or Burress, but neither player is very dynamic, and both will have trouble getting open against the quicker defensive backs in the league.

The Steelers need receiving options to fit the quick-passing attack of Todd Haley’s offense and should look to address this via free agency and the draft.

Offensive Line Depth

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The Steelers offensive line actually looks pretty good heading into the 2013 season—that is if their recent draft picks develop as anticipated.

From left to right, the Steelers have Marcus Gilbert, Ramon Foster, Maurkice Pouncey, David DeCastro and Mike Adams.

That is a young, athletic group with tremendous upside. Once they play together as a unit, the offensive line should finally become a strength of the team.

But with the young linemen stepping into the starting lineup, the Steelers will now lack depth.

Colon has already signed with the New York Jets, and both Max Starks and Doug Legursky are still free agents. Without these players, the Steelers are without two starters and their top interior backup from last season.

As it stands now, Kelvin Beachum is the top backup on the line, where he will be expected to play both tackle and guard, while John Malecki will take over for Legursky as the backup center and guard.

Beyond these two players, the Steelers are very thin along the offensive line.

With so many needs elsewhere on the roster and so many draft picks spent on the offensive line in recent years, the Steelers may not want to spend more picks on the position this year. This means they need to find depth for the offensive line in free agency.

There is a remote possibility that either Starks or Legursky—or both—could return, which would not be a bad solution.

Regardless of who they sign, the Steelers will need at least one more lineman who can provide quality depth at both guard and tackle.

By signing this type of player, they can concentrate on other more pressing needs in the draft.

Linebacker Depth

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With James Harrison, Stevenson Sylvester and Brandon Johnson on the way out—yes, the first player mentioned is by far the most important—the Steelers are in need of upgrading their depth at linebacker.

Harrison’s departure leaves the Steelers with a hole at right outside linebacker that they expect Jason Worilds to fill.

Sylvester was a nonfactor at inside linebacker, but Johnson could play both inside and outside.

The Steelers already expressed interest in Dan Connor but did not sign him. Still, they are clearly interested in adding depth.

On the outside, the Steelers currently have Chris Carter and Adrian Robinson—who flashed some pass-rushing ability last preseason—as their top two options with the injured Sean Spence on the inside.

Given their history, it’d be far more likely that the Steelers add an inside instead of an outside linebacker through free agency since they like to develop their own pass-rushers.